Built-up Edge Research Articles

An integrative approach to coating/carbide substrate design of CVD and PVD coated cutting tools during the machining of austenitic stainless steel

Machining of hard to cut materials such as austenitic stainless steel presents a challenge due the thermo-mechanical properties of this material, which contribute to intensive buildup edge formation and negatively affect tool life. CVD TiCN + Al2O3 and PVD AlTiN coatings deposited on cemented carbide substrates are generally recommended for machining austenitic stainless steel. These coatings were deposited by two different methods: (i) PVD AlTiN was deposited on the same substrate material at two different thicknesses (2.5 and 5 μm); (ii) CVD TiCN + Al2O3 was deposited with the same thickness (5 μm) on two different substrates. A new approach to applying various PVD and CVD (coating + substrate) integrated systems is introduced in this study for austenitic stainless steel machining. The relationship between the coating and substrate characteristics of these material systems and tool performance was assessed. The characteristics of the coating/carbide substrate design were evaluated in terms of chemical, phase composition, architecture, mechanical properties in relation to the tribological and wear performance. The obtained results demonstrate an improvement in tool wear performance and tool life brought about by the surface engineered layer/carbide material with an optimal combination of coating/substrate properties. Based on these findings, a guideline is proposed for further study of the cutting tool life and wear performance of CVD and PVD coated cemented carbide inserts.

The effect of cryolite on grinding of stainless steel

Abstract Active fillers play a major role in the dry grinding of stainless steel. However, the mechanism altering the process is still unknown. In this work, the efficiency of cryolite as filler was studied with a pin-on-disk tribometer. Simplified coated abrasives with and without active filler were used to reduce possible non-cryolite related interactions to a minimum. Diffusion experiments with stainless steel pins and cryolite were performed and the change in efficiency during abrasion investigated. The analysis of the pins revealed a FexCr1-xF2 phase. Tensile tests were performed of heat-treated specimens to investigate changes in brittleness. Finally, dissolution experiments were conducted, which proved a decrease in built-up edge volume in presence of cryolite, leading to a higher cutting efficiency.

Identification of the "Snowflakes" on the Machined Surface of the AlSi10Mg Alloy Casting

The usage of aluminium alloys has an increasing trend in the manufacturing industry in recent years. This fact is connected with their ability to combine their very good properties. Characteristics of aluminium are low specific weight, very good thermal and electrical conductivity, and ductility. However, the major disadvantages are low strength and hardness. Therefore the aluminium alloys are alloyed with the elements, which would significantly improve the properties of aluminium. The machining process of aluminium alloys is influenced by many factors that affect the machinability. These factors are for example process conditions, cutting tool material, cutting tool geometry, cutting environment or the chemical composition of the machined material itself and microstructure of the workpiece. Due to the different structures, the machinability of aluminium alloys and pure aluminium is significantly different. Factors such as chemical composition, precipitates, the number and position of soft particles or the strain hardening degree affect the behaviour between the cutting tool and the workpiece during machining. When machining the aluminium alloys, there are some problems such as the surface quality, micro-geometry, tool wear, the chip shape, built-up edge formation, etc. The article deals with the surface defect investigation after the machining process, when on the surface of the material stay the visible snowflakes after the turning operation. These snowflakes were documented and were performed analysis and observation to find the cause of these flakes.

Surface roughness at facing on a lathe

It is known that during the facing on a lathe, due to the cutting speed change along the workpiece radius, the generation of the built-up edge is possible. Because of this fact, a maximum of the surface asperities height could be highlighted. From the practical point of view, it is important to have information concerning the influence exerted by some input factors of the facing process on the values of the roughness parameters that corresponds to the surfaces obtained by such a machining process. An experimental research was designed and materialized to evaluate the influence exerted by the cutting speed, feed rate and turning tool corner radius on the values of the surface roughness parameters Ra and Rq. By mathematical processing of the experimental results, some empirical mathematical models were determined. One confirmed that a low value of the surface roughness could be obtained by using high turning speed and adequate values for the feed rate and turning tool corner radius.

Effects of eco-friendly cooling strategy on machining performance in micro-scale diamond turning of Ti–6Al–4V

Abstract Titanium alloys are difficult-to-cut materials due to their low elastic modulus and poor thermal conductivity. To deepen the understanding of the cutting performance for Ti–6Al–4V under various eco-friendly cooling conditions, surface integrity, cutting forces, and tool wear were comprehensively investigated through cutting experiments implementing three cooling methods, namely, cryogenic gas (CG), minimum quantity lubrication (MQL), and a combination of CG and MQL (CG + MQL), respectively. The results show that the lowest surface roughness ( S a = 76.71 nm) was achieved at a low spindle speed under the CG + MQL cooling conditions. This suggests that of the three cooling methods, the CG + MQL hybrid cooling method achieved the highest cooling efficiency. Compared with the MQL cooling method, the CG + MQL cooling method led to more pronounced tool wear and material adhesion due to reduced oil-based lubricity caused by low temperatures. Under the MQL cooling conditions, the elastic recovery of Ti–6Al–4V accelerated the formation of micro-cleavages on the clearance face of the diamond tool. Additionally, the depth of cut was also comparable to the tool edge radius in the micro-scale diamond turning. Compared with the conventional turning of Ti–6Al–4V, this round-edge effect, combined with the adhesion and built-up edge, led to a relatively stronger friction effect, evidenced by an increase in the coefficient of friction from 1.027 to 3.532, and higher specific cutting energy under all the cooling conditions in micro-scale diamond turning.

Machining of Inconel 718 Using Coated WC Tool: Effects of Cutting Speed on Chip Morphology and Mechanisms of Tool Wear

Inconel 718 is a nickel-based superalloy extensively used in aerospace industries for its excellent physical, mechanical and chemical properties. Poor thermal conductivity, high toughness and strong work hardening tendency of this alloy adversely affect its machinability. Inconel 718 is therefore treated as ‘difficult to cut’ or ‘hard to cut’. Conventional machining of Inconel 718 faces various challenges like high cutting forces, evolution of huge cutting temperature and rapid tool wear. As a consequence, surface integrity of the machined part becomes disappointing. Excessive tool wear incurs additional cost of tool replacement. To overcome machining difficulties of this alloy, application of coated tool insert is recommended. To this end, the present work attempts to investigate machining performance of Inconel 718 using coated carbide (cemented carbide) tool with chemical vapour deposition multi-layer coating TiN/TiCN/Al2O3/TiN (TN4000) under dry cutting environment. Turning experiments are conducted with varied cutting speeds: 50, 75, 100 and 125 m/min at constant feed rate 0.1 mm/rev and constant depth of cut 0.4 mm. Chip morphology including features of chip cross section, free surface of chip and chip reduction coefficient as affected by cutting speed is studied herein. Abrasion, adhesion, chipping off, coating delamination, built-up edge formation, diffusion, etc. are identified as potential wear mechanisms. In addition to flank wear and crater wear, occurrence of notch wear is also distinctly identified. Surface roughness of the finished work part is found better in case of coated tool than uncoated one. Coated tool corresponds to lesser cutting force magnitude, lower cutting temperature and higher value of chip reduction coefficient than the case of traditional uncoated tool.

Effect of different machining parameters on surface roughness of aluminium alloys based on Si and Mg content

Aluminium-based alloys are considered lengthily for many applications in engineering areas due to their good mechanical properties. Machining these alloys had attracted the attention of many researchers on how to improve the machining, especially when high manufacturing rate is demanded. Usually, machining these materials poses some difficulties such as burr formation, roughness of the surface, continuous chip formation and build-up edge on cutting edge. In this study, AA6061T6, LM6 and AA5083 aluminium-based alloys were considered to research the optimum drilling parameters with the aim to address the earlier started challenges. Drillings were carried out by using a MAHO three-axis CNC drilling machine with an HSS drilling bit at three different spindle speeds and feed rates. From the results, it was established that each aluminium alloy has different surface roughnesses and this surface roughness decreases as spindle speeds increased. A minimum build-up edge was achieved for AA5083 and AA6061T6 alloys. However, a relatively high BUE was noticed in LM6.

Difficulties in the Machining Super Duplex Stainless Steels

Abstract Super duplex stainless steels are used in increasingly more areas. The machinability of duplex stainless steels is generally poor. We performed dry turning tests on G X2CrNiMoCuN 26-6-3-3 casted superduplex steel, using two different PVD coated cutting inserts. One of them was coated with TiAlN and other with TiAlSiN. Strong burr and built-up edge formation were observed during our machining experiments; these damaged the edges of the tools. The shortened tests did not show significant difference betwen the effect of the coatings.

Investigation of cutting tool wear behaviors in machining of silicon carbide and magnesium oxide reinforced aluminum 2024 matrix composites

In this study, first Silicon Carbide (SiC) and Magnesium Oxide (MgO) powders of ≤105 micron particle size were mixed in equal amounts. Then, the powder mixture was reinforced by using vortex method in liquid Al2024 aluminum alloy in three different ratios (3%, 6% and 12%) to produce composites. Finally, on composite samples, machinability tests were carried out with a uniform cutting tool at constant cutting depth (1 mm) and dry cutting conditions. Three different cutting speeds (100, 150, 200 m min−1) and three different feed values (0.03; 0.06; 0.12 mm/rev) were used in the machining experiments. Machinability tests were performed on a Computer Numerically Controlled (CNC) lathe. Wear behavior of cutting tools were examined by using SEM microscope images. In all of the cutting tools, built-up edge (BUE) was observed while small amount of flank wear occurred. It was concluded that the selected cutting tool and cutting parameters may be suitable for the machining of such composite materials.

Effect of metallurgical parameters on the drilling and tapping characteristics of aluminum cast alloys

The present study was performed on an Al-6% Cu-0.7%Si alloy, and 319 and 356 alloys following different heat treatments. The main task was to evaluate the drilling and tapping characteristics of the Al-Cu alloy with respect to the Al-Si-based 319 and 356 alloys. The drilling work was carried out on a Huron K2X8five CNC machine at 15,000 rpm with continuous cooling to absorb the heat and to clean the holes from the chips formed during the drilling operation. The results show that the addition of Si coupled with T6 aging treatment produces the highest cutting forces (about 360 N) among the alloys studied (approximately 270 N) after 2500 holes. Considering the Al-Cu-based alloys, varying the aging treatment has practically no significant bearing on the cutting forces. Apparently, a high Cu content acts as a self-lubricant, facilitating the drilling process up to 2700 holes, with no sign of tool wear. However, due to the low level of Si in the Al-Cu-based alloy, built up edge (BUE) is more frequent, with conical chips, which would affect the precision of the size of the drilled hole. The chips are normally dull and characterized by their rough surfaces compared to those obtained from A356.0 alloy. Tapping of the drilled holes was carried out using Guhring 971 H6 M6 6HX- HSSE taps. The HT200-based alloys revealed excellent machinability with no sign of tool wearing after 2500 holes. In contrast, the tool failed after 1600 holes in the case of 356 alloy and 2160 holes for 319 alloy. Thus, it is concluded that the presence of 3.5% Cu in the 319 alloy helped in reducing the severity of wearing due to eutectic Si particles. However, the tapping forces reached 120 N prior to failure compared to about 75 N in the case of T200-based alloys.

Research on Chip Shear Angle and Built-Up Edge of Slow-Rate Machining EN C45 and EN 16MnCr5 Steels

One of the phenomena that accompanies metal cutting is extensive plastic deformation and fracture. The excess material is plastically deformed, fractured, and removed from the workpiece in the form of chips, the formation of which depends on the type of crack and their propagation. Even in case of the so-called ‘continuous’ chip formation there still has to be a fracture, as the cutting process involves the separation of a chip from the workpiece. Controlling the chip separation and its patterning in a suitable form is the most important problem of the current industrial processes, which should be highly automated to achieve maximal production efficiency. The article deals with the chip root evaluation of two EN C45 and EN 16MnCr5 steels, focusing on the shear angle measuring and built-up edge observation as important factors influencing the machining process, because a repeated formation and dislodgement of built-up edge unfavorably affects changes in the rake angle, causing fluctuation in cutting forces, and thus inducing vibration, which is harmful to the cutting tool. Consequently, this leads to surface finish deterioration. The planing was selected as a slow-rate machining operation, within which orthogonal and oblique cutting has been used for the comparative chips’ root study. The planned experiment was implemented at three levels (lower, basic, and upper) for the test preparation and the statistical method, and regression function was used for the data evaluation. The mutual connections among the four considered factors (cutting speed, cutting depth, tool cutting edge inclination, and rake angle) and investigated by the shear angle were plotted in the form of graphical dependencies. Finally, chips obtained from both steels types and within both cutting methods were systematically processed from the microscopic (chip root) and macroscopic (chip pattern) points of view.

Influence of process parameters on the cutting performance of SiAlON ceramic tools during high-speed dry face milling of hardened Inconel 718

Heat-resistant superalloys (HRSAs) exhibit excellent mechanical strength and structural stability at elevated temperatures. Hence, aerospace and power industries have consistently chosen nickel-based superalloys over the years for manufacturing hot-section components. However, poor machinability of these alloys has always been a challenge. This paper investigates the cutting performance of new-generation SiAlON ceramics under extreme conditions of dry high-speed face milling of hardened Inconel 718. Comprehensive characterization of the ceramic tool and its milling performance were conducted using instrumented micro/nano-mechanical indentations, tool life studies, optical 3D imaging, and SEM/EDS investigation of wear patterns. Also, experimental results were linked to the finite element analysis (FEA) of temperature and stress profiles. It is demonstrated that a few major factors govern the ceramic tool life under the outlined cutting conditions: (1) High temperature at the cutting edge exceeding 1250 °C. This temperature is close to the melting point of Inconel 718, and moreover, it is highly localized around the cutting edge-chip interface. (2) High resultant mechanical stress on the tool of around 5.8 GPa. (3) Thermal and mechanical fatigue loading due to the discontinuity of the milling process, combined with (4) intensive built-up edge formation caused by severe weldability of the softened workpiece to the tool. Combination of these phenomena results in a significant change in the machinability of the workpiece material after surpassing a certain limit of cutting speed. The cutting forces, tool wear, and chipping show a significant decline with increasing the speed high enough, which is attributed to the change in the material properties of the workpiece and dissolution of the hard particles within the Inconel microstructure.

Self-lubricating TiN/MoN and TiAlN/MoN nano-multilayer coatings for drilling of austenitic stainless steel

Self-lubricating TiN/MoN and TiAlN/MoN nano-multilayer coatings were fabricated on the HSS drills by a closed field unbalanced magnetron sputtering system. The as-deposited TiN/MoN and TiAlN/MoN nano-multilayer coatings exhibit a face-centered cubic structure with (200) and (111) preferred orientation, respectively. The TiN/MoN coating possessed higher hardness of 31 GPa than that of TiAlN/MoN coating (21GPa). Both of the TiN/MoN and TiAlN/MoN coating exhibit low coefficient of friction with values of about 0.32. The cutting force and temperature of cutting edge of TiN/MoN and TiAlN/MoN coated drills were remarkably decreased compared to uncoated drills during the dry drilling test in austenitic stainless steel. The numbers of drilling holes of TiN/MoN and TiAlN/MoN coated drills were 4.2 and 2.4 times larger than that of uncoated HSS drills. The build-up edge was avoided on TiN/MoN and TiAlN/MoN coated drills which resulted in better surface quality of drilled holes compared to uncoated HSS drills.

Effect of cutting parameters on tool wear under minimum quantity cooling lubrication (MQCL) conditions

This paper presents the effect of cutting parameters on tool wear under minimum quantity cooling lubrication (MQCL) conditions. Turning AISI 304 stainless steel was carried out using VAMF-1 environmentally friendly cutting fluid under MQCL conditions, for which 27 groups of all-factor experiments were utilized. The tool wear results showed that the most effective parameter was the cutting speed (relative contribution of 46.725%), followed by the feed rate (relative contribution of 28.120%). According to the tool vibration results, the cutting speed was the most important parameter, followed by the feed rate and the cutting depth. During low-speed cutting, a larger feed rate and cutting depth could be selected, for which adhesive wear is the prevailing mechanism. As the cutting speed increased, the built-up edge (BUE) near the cutting edge disappeared and the adhesives fell off; diffusion wear was the main mechanism in this case. In addition, a prediction model was constructed with the objective of surface finish and tool wear, and the results were optimized by an improved fruit fly optimization algorithm (FOA). The verification experiment results showed that the prediction errors of VB and Ra were 2.15% and 6.48%, respectively. Moreover, MQCL achieved better surface quality and lower tool wear than minimum quantity lubrication (MQL) and dry cutting under the optimized parameters.

Experimental investigation on boring of HSLA ASTM A36 steel under dry, wet, and cryogenic environments

ABSTRACTAn endeavor has been made to bailiwick cryogenic, wet, and dry boring of HSLA ASTM A36 steel, which is predominantly used in armor material and oil and gas pipelines. To ensure a direct coolant supply (controlled flow rate) at the cutting zone and palpable ciphering of cutting temperature, a transmogrified boring bar is exercised. Electrical discharge machining (EDM) was availed to create for the accommodation of a thermocouple slot, in an axial hole boring bar. Reduction of 16.1–59.8% and 4.3–16.7% in cutting force, 53.38–78.36% and 25.31–64.89% in cutting temperature, and 27.76–70.23% and 4.22–28.30% in surface roughness is ascertained in cryogenic milieu boring in correlation to dry and wet milieu boring, respectively. It is discerned for cutting force, speed of 88.59 m/min and 0.055 mm/min is the ideal cutting parameter for cryogenic, wet and dry boring conditions. For cutting temperature, ideal cutting parameter is speed of 88.59 m/min and 0.048 mm/min for dry and wet, respectively, and speed of 88.59 m/min and 0.055 mm/min for cryogenic boring. Additionally, speed of 88.59 m/min and 0.055 mm/min is the ideal cutting parameter for surface roughness in all three different cutting environments. From ANOVA, it is determined that speed plays a vital role in all three conditions of boring. For dry and wet boring, speed personates a notable semblance in ascertaining the cutting temperature, but in the case of cryogenic boring, feed plays an imperative part. Additionally, for surface roughness, feed is the most prominent parameter in cryogenic, wet, and dry boring. Furthermore, cryogenic machining surges the hardness of ferrite culminating in curtailed chip lengths and deficient built-up edge evolution on the cutting tool. An abatement in flank wear by 36.58% and 53.65% is ascertained in the cryogenic boring of ASTM A36 HSLA steel correlated to wet and dry boring, respectively. Boring under cryogenic condition, the crater wear reduces by 88.30% and 90.10% with respect to wet and dry boring, respectively. Scanning electron microscopy observations of bored surfaces in wet and dry boring show a network of microcracks which is absent in cryogenic boring of ASTM A36 HSLA steel. Compressive residual stress has increased by 9.5% and 31.83% in boring under cryogenic medium with respect to wet and dry boring of ASTM A36 HSLA steel. There is an overall increase in hardness value in bored surface in cryogenic medium over wet and dry bored surface by 22.26%–30.06% and 21.06–39.43%, respectively. The corrosion resistance in cryogenic boring increases by 65.26% and 29.33% with respect to wet and dry boring of ASTM A36 HSLA steel, respectively. High repercussions of geometrical features are ascertained in abatement of circularity and cylindricity of hole profile bestowing cryogenic medium of boring.

Influence of cutting parameters on cutting forces and surface roughness in dry turning of Al using PCD and different coated tools

Aluminium (Al) is the suitable material for aerospace and automotive industries due its light weight, corrosion resistance, weldability, non-magnetic and mechanical properties. But, machining of Al and its alloy and finding the suitable tool is really a big challenge because of its formation of BUE (Built-up Edge) and BUL (Built-up Layer). This paper presents the influence of cutting parameters (speed, feed and depth of cut) and its effect on the cutting force and the surface finish. Five different advanced cutting tool inserts (SPUN WC, SPGN WC, PCD, WC + TiN and WC + Ti(C, N) TiN + Al2O3) at different cutting speed (Vc) ranging between 300 m/min and 700 m/min and feed rate (f) of 0.045, 0.06, 0.09 and 0.125 mm/rev at a depth of cut of 0.2 mm (constant throughout the experiment) were taken for the experiment. Tool inserts were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. The cutting forces were measured using Kistler force dynamometer. Amongst all tools, PCD provided a better result in all aspects but surprisingly WC tool provided a better surface finish with lesser tool wear. For all cutting conditions, high speed (670 m/min) and low feed rate (0.045 mm/rev) were recommended.

Improving nanocutting surface quality by force-controlled rolling

Force-controlled rolling method which is a combination of rolling tool, force sensor and fast tool servo is proposed to realize real-time control of rolling force in surface modification process. Especially when the surface is complex, the rolling force can be changed dynamically based on the surface profile and the rolling path. Therefore, the machinability of soft material, such as lead (Pb), are easy to be modified by force-controlled rolling. After the soft and sticky workpiece, lead, is modified, the surface of it becomes hard enough to suppress the scratch of the chips, the formation of built-up edge, and the side flow of the workpiece material at the subsequent nanocutting process. Nanocutting of Pb mirrors validates the effectiveness of the force-controlled rolling method. Besides that, side flow region under the action of the tool edge and its evolution after the formation of build-up edge is investigated.

Effects of WC grain size and Co content on microscale wear behavior of micro end mills in aluminum alloy 7075 machining

The effects of cemented carbide materials on cutting edge fracture mechanism of micro end mills in aluminum alloy 7075 machining are investigated. A series of micro milling experiments on the tool wear were conducted. The surface morphologies of micro end mills were observed, and the end teeth flank wear length and tool total cutting edge length reduction were measured. The results showed that the Co content and WC grain size of cemented carbides have significant effects on tool wear and cutting performance of the micro end mill. With increase of WC grain size, the tool end teeth flank wear length increases and the total cutting edge length reduction of the mill obviously increases. Thus, the micro end mill with finer grain size presents better wear resistance. However, with increase of Co content, the micro end mill exhibits less wear resistance. This can be explained that the adsorption energy between Co atom and Al atom become larger based on first principle calculation of adsorption energy between cemented carbides and aluminum alloy. The Co binder of tool material is dragged off by frequent fall off of built-up edge, resulting in more loss of Co element. Thus, the strength of the tool is decreased.

Influence of Different Cooling Methods on Tool Life, Wear Mechanisms and Surface Roughness in the Milling of Nickel-Based Waspaloy with WC Tools

Superalloys are generally considered to be difficult to machinability. In recent attempts to facilitate their machinability, minimum quantity lubrication (MQL) has been used due to its positive influence on cutting tool life, the environment and human health. This study focused on the tool life, wear behavior and surface roughness in the milling of nickel-based superalloy Waspaloy. Uncoated carbide tools, PVD (TiAlN)-coated tools and CVD (TiCN + Al2O3 + TiN)-coated tools were used. Experiments were performed with different cooling methods which included dry, wet and MQL. SEM and EDX were used for tool wear behavior and mechanism analyses. A portable measuring instrument and a 3D optical profilometer were employed for surface roughness analyses. Results obtained from the tests showed that during the milling of the Waspaloy, adhesion and abrasion were effective wear mechanisms for the cutting tools. The main wear behaviors were flank wear, crater wear and BUE (built up edge). In addition to these results, reduction in the tool wear, the wet machining and machining with the MQL system provided improvement at the rates of 37.54% and 29.01%, respectively, when compared to the dry machining.

Experimental Study of Microgroove Surface Using Three-Dimensional Elliptical Vibration Texturing

This paper presents our preliminary study of the microstructured surface on microgrooves patterns, which have manufactured using the three-dimensional elliptical vibration texturing (3D-EVT) method. The 3D-EVT method uses a three-dimensional trajectory of elliptical locus of the cutting tool tip in high vibration frequency to fabricate the microstructure or the vibration mark pattern on the machined surface. The experimental study has been done with a variation of the nominal cutting speeds from 300 to 600 mm/min. The preliminary results showed that in the low nominal cutting speed of 300 and 450 mm/min, the microstructured surfaces were not manufactured well due to the bulging existence on the microstructured surface in which it is correlated with the build-up edge phenomena. On the other hand, a relative excellent microstructured surface can be achieved at the higher nominal cutting speed of 600 mm/min. In addition, a lubricant could be used to obtain an excellent microstructured surface to avoid the built-up edge phenomena.